1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods for treating a surface having an exposed silicon/silicon dioxide interface, which treatment is useful in the manufacture of semiconductor devices. The methods are particularly useful for a post chemical mechanical polishing clean of a surface having an exposed silicon/silicon dioxide interface.
2. The Relevant Technology
Chemical mechanical polishing is finding increasing application in the manufacture of semiconductor devices to planarize surfaces in preparation for high resolution photolithography and for other purposes. Chemical mechanical polishing involves polishing an uppermost film on the surface of a semiconductor substrate by use of a polishing pad and a polishing slurry. The slurry contains polishing particles. Pad types and slurry compositions vary depending on the material being polished and other factors.
In the context of this document, the term xe2x80x9csemiconductor substratexe2x80x9d is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term xe2x80x9csubstratexe2x80x9d refers to any supporting structure including but not limited to the semiconductor substrates described above.
Chemical mechanical polishing is particularly useful where feature sizes of less than 0.5 micron must be defined over a topography already existing on the substrate surface. In such circumstances, a reflowed silicon dioxide glass layer is insufficiently planar, but with chemical mechanical polishing, sufficient planarity may be achieved to facilitate high resolution photolithography. Chemical mechanical polishing may also be employed to completely remove portions of a layer being polished, so that underlying material is exposed. In either case, a clean step is required after the chemical mechanical polishing to clean polishing slurry from the substrate surface.
Where silicon dioxide or silicon is the layer being polished, the polishing slurry typically contains silicon dioxide particles having an average size of about 30 nanometers (nm). The silicon dioxide particles that remain on a silicon dioxide surface after polishing are typically removed by a clean process including an HF (hydrofluoric acid solution) dip followed by a deionized water rinse. Silicon dioxide particles and other contamination remaining on a silicon surface after polishing are typically cleaned in an ammonium hydroxide solution or the like.
Where a silicon dioxide layer is polished until some silicon is exposed, or where a silicon layer is polished until some silicon dioxide is exposed, the above typical clean processes can result in problems. While the typical clean process for silicon dioxide is effective to remove silicon dioxide particles from a silicon dioxide surface, a silicon surface is not adequately cleaned. Silicon dioxide particles tend to collect on the silicon surface and, once the clean process is complete, tend to permanently adhere there, regardless of further cleans. The typical clean processes for silicon are likewise ineffective to remove silicon dioxide particles from a silicon dioxide surface. Further, an ammonium hydroxide clean, which etches silicon, can be unacceptable where particularly fine or small silicon structures must be preserved. Accordingly, there exists a need for a clean process which can remove silicon dioxide particles from both silicon dioxide and silicon surfaces, and particularly without etching silicon surface.

In accordance with the present invention, a method is presented for treating an exposed silicon/silicon dioxide interface on a surface situated on a semiconductor substrate. The interface is exposed by a chemical mechanical polishing step. The interface is next contacted with a solution composed, by volume, of 200 parts of deionized water, 1 part of hydrofluoric acid, and at least 5 parts of tetramethyl ammonium hydroxide.
The interface is again contacted with an organic carboxylic acid surfactant having a critical micelle concentration greater than or equal to 10xe2x88x927 m/l. The organic carboxylic acid surfactant, which can having a pH greater than or equal to 4, can effectively clean the interface. The critical micelle concentration greater than or equal to 10xe2x88x927 m/l of the organic carboxylic acid surfactant significantly prevents the formation of a charge differential between the silicon dioxide and silicon portions of the surface, which charge differential would otherwise cause any silicon dioxide particles present to remain on the silicon portions of the surface. The surfactant properties of the selected organic carboxylic acid helps to remove any silicon dioxide particles from the surface. The organic carboxylic acid surfactant can be pentadecanoic acid or other similar long chain acids. A preferred organic carboxylic acid surfactant is citric acid.
Lastly, silicon dioxide particles are removed from the interface by optionally contacting the same with deionized water or sulfuric acid. The deionized water or sulfuric acid removes the organic carboxylic acid surfactant from the surface, leaving a clean surface with fewer particulate matter on both the silicon dioxide and silicon portions thereof, with substantially no etching of the silicon portion.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.